1 Introduction

GNU Libidn is a fully documented implementation of the Stringprep,
Punycode and IDNA specifications. Libidn’s purpose is to encode and
decode internationalized domain name strings. There are native C, C#
and Java libraries.

The C library contains a generic Stringprep implementation. Profiles
for Nameprep, iSCSI, SASL, XMPP and Kerberos V5 are included.
Punycode and ASCII Compatible Encoding (ACE) via IDNA are supported.
A mechanism to define Top-Level Domain (TLD) specific validation
tables, and to compare strings against those tables, is included.
Default tables for some TLDs are also included.

The Stringprep API consists of two main functions, one for converting
data from the system’s native representation into UTF-8, and one
function to perform the Stringprep processing. Adding a new
Stringprep profile for your application within the API is
straightforward. The Punycode API consists of one encoding function
and one decoding function. The IDNA API consists of the ToASCII and
ToUnicode functions, as well as an high-level interface for converting
entire domain names to and from the ACE encoded form. The TLD API
consists of one set of functions to extract the TLD name from a domain
string, one set of functions to locate the proper TLD table to use
based on the TLD name, and core functions to validate a string against
a TLD table, and some utility wrappers to perform all the steps in one
call.

The library is used by, e.g., GNU SASL and Shishi to process user
names and passwords. Libidn can be built into GNU Libc to enable a
new system-wide getaddrinfo flag for IDN processing.

Libidn is developed for the GNU/Linux system, but runs on over 20 Unix
platforms (including Solaris, IRIX, AIX, and Tru64) and Windows. The
library is written in C and (parts of) the API is also accessible from
C++, Emacs Lisp, Python and Java. A native Java and C# port is
included.

Also included is a command line tool, several self tests, code
examples, and more.